December 21, 2012
We all know water freezes to ice at 32 degrees Fahrenheit. But that isn’t always the case. When water is very pure, with nothing to seed the formation of ice crystals, it can remain liquid at much lower temperatures. This supercooled state is of intense interest to scientists who are studying the fundamental behavior of water, which despite its simple structure has many unusual properties.
For example, water is denser in liquid than in solid form, it has a high boiling point compared to many other liquids, and the high degree of "surface tension" formed at water's surface allows some creatures – including insects and lizards – to actually walk on water.
One particular temperature range for supercooled water, from about minus 42 degrees to minus 215 degrees Fahrenheit, has been dubbed no-man’s land. Near the top of this range, water crystallizes into ice so rapidly that it can be difficult to observe the molecules that remain in liquid form. At the colder end of the range, it forms a glassy, non-crystallized solid.
Water’s many unusual properties become even more exaggerated at these temperature extremes. Yet directly observing the transformation of water molecules in no-man’s land has proven challenging for scientists.
Anders Nilsson, a professor of photon science at SLAC and Stanford University, said scientists have been trying to push their observations of water to lower and lower temperatures. Based on the way water's unusual properties trend at warmer temperatures, they expect to see a "mysterious" and "unknown" transformation of water at about minus 49 degrees Fahrenheit, he said.
To better understand this transformation and water's other unusual properties, "it's important that we can study water in the no-man's regime," Nilsson said.
Nilsson has been using SLAC's Linac Coherent Light Source for experiments that seek to shed more light on the properties of liquid water within no-man's land.
The phrase "no-man's land" came into common usage after author Ernest Dunlop Swinton's 1914 description of the corpse-filled middle ground of World War I trench warfare as a "dreadful 'No-Man's-Land' between the opposing lines." The phrase, published in Swinton's short piece, "The Point of View," has since been broadly used to describe any restricted, disputed, unoccupied, uninhabitable, undesirable or ambiguous area.
H. Eugene Stanley, a physics and biomedical engineering professor at Boston University, is credited with assigning the phrase in the early 1990s to a temperature range for supercooled water.